The present invention relates to a wafer surface observing apparatus for optically inspecting foreign materials, flaws, defects, contamination, and so on (hereinafter collectively referred to as foreign matter) present on the surface of an object to be inspected and, more particularly, to a technique for observing and inspecting end portions of parts formed like flat plates such as silicon wafers, semiconductor wafers, glass substrates, or the like.
A surface observing apparatus or surface inspection apparatus for inspecting the surfaces of semiconductor wafers is shown, for example, in JP-A-2005-156537.
A wafer surface observing apparatus detects foreign matter present on the surface of a semiconductor wafer by illuminating the surface of the semiconductor wafer with an optical beam such as laser light and detecting reflected light or scattering light produced on the surface of the wafer by a photodetector.
The area on a wafer surface that can be inspected is a region excluding end portions of the wafer, irrespective of whether a pattern is formed on the surface. The end portions of the wafer indicate edges having angles produced by sawing a silicon wafer into a flat plate as well as marginal regions where a chip is not completely formed.
Since edge portions of wafer end portions have angles to the surface, reflected light or scattering light produced from the light hitting the edge portions is not incident on the photodetector. Furthermore, in marginal portions where a chip is not completely formed, film residues, delamination, and so on often occur. Reflected light or scattering light produced from the illuminating light is diffusively reflected greatly. This deteriorates the detection sensitivity of the surface observing apparatus.
Therefore, the inspected region set heretofore has excluded wafer end regions. As wafers having increased diameters are manufactured, chips are often fabricated almost up to marginal regions. It is highly likely that film residues, delamination, and so on at end portions of wafer constitute foreign matter on the surfaces of the wafers. This has greatly affected the yield.
In the past, an optical microscope has been used as a means for checking whether foreign matter on the surface of a defective wafer detected by a surface observing apparatus has been affected by roughening at ends of the wafer. With the optical microscope, observation and comparison have been made to clear up the cause (cause-effect relationship).
Therefore, an exorbitantly long time has been taken to find the cause. This has resulted in a delay in applying feedback to the process. The delay in applying feedback to the process retards yield improvement.